Television scanning system



Aug. 19, 1941. M. K. TAYLOR I TELEVISION SGANNING SYSTEM Filed Sept. 25,1939 ATTORNEY fiection is Patented Aug. 19, 1941 UNITED STATE s PATENTOFFICE 2,253,355 'rELEvrsroN scANNnvc sYs'rEM Maurice K. Taylor,

Application .September In Great Britain This invention relates totelevision scanning systems and more particularly to such systemscomprising cumulative deflection of a cathoderay beam by means of anelectromagnetic scanning'eld and an electrostatic scanning neld.

In conventional television receivers, it has been the practice toprovide scanning o! thelcathoderay beam of the cathode-raysignal-reproducing device in one direction by means of either anelectromagnetic scanning field or an electrostatic scanning held. Due tothe tact that the lengths of the cathode-ray tubes heretofore in generaluse are great in comparison with their screen diameters, the cabinets oitelevision receivers in' which `such tubes are horizontally disposedtherein have, of necessity, been quite'large. 'This diinculty has beenovercome to some extent by -Hollinwoom England, assigner .to HazeltineCorporation,

a corporation of Dela- 23, 1939, Serial N0. 296,220

September 24, 1938 8 Claims.l 5,(Cl. P18-7.5)

arranging the cathode-ray tube vertically, but I this has necessitatedthe use of a viewing mirror. To avoid these disadvantages, shortercathoderay tubes have been produced with a view to reducing both thebulk andthe cost of-the cabinets required `'to accommodate them.lHowever.

vthese shortertubes have the disadvantage of Furthermore, the energyrequired to provide a given deiiection'by a neld oi one given typevaries approximately as vthe square of the deflection. For this reasonthe energy requirements are considerably reduced if a part of therequired deprovided by a neld of one type and the remainder ofthe-required deflection is provided by a field of the other type.

the dpresent invention, thereimproved television scanning It is anobject o! fore, to provide an system which is not theAabove-mentionedfdisadvantages o! the arrangements ci the prior art.

. It isa further object'oi` the presentinvention to provide an improvedtelevision scanning systern which provides simultaneouslyelectromagnetlc and electrostatic scanning nelds which are cumulativeiinv theirdefiecting action en the cathode-ray beam.

`such high ilux values when the time ratio is high.

In accordance with the invention, a television scanning system fordenecting a cathode-ray beam comprises an oscillation generator,electromagnetic scanning windings, and means including the generator forproducing a current oi substantially saw-tooth wave form in theelectromagnetic scanning windings. There are also provided electrostaticscanning plates and .means including the same oscillation generator forsupplying thereto, simultaneously with the application of said saw-toothcurrent to said electromagnetic scanning windings, a scanning voltage ofsubstantially saw-tooth wave form and of periodicity the same as theabovementioned sawtooth current. The electromagnetic scanning windingsand the electrostatic scanning plates are relatively positioned andexcited to providel a cumulative deection of the cathode-ray beam.

For agbetter understanding of the invention, together with other andfurther objects thereof, reference is had to the following descriptiontaken in connection with the accompanying drawing alncilnilts scope willbe pointed out in the appended c a s.

In the accompanying drawing, Fig. 1 is acomplete circuit diagram, partlyschematic, o! a television receiving system including a scanning systemin accordance with the present invention, whileFigs. 2, 3, and 4 arecircuit diagrams oi' different embodiments of the scanning system of theinvention.

Referring now more particularly to Fig. 1 of the drawing, the systemthere illustrated comprises a receiver oi the superheterodyne typeincluding an antenna system i0, Il connected to a radio-frequencyampliner I2 to which is connected in cascade, in the order named, anoscil-v lator-modulator I3, an intermediate-frequency amplifier Il, adetector Il, a video-frequency ampliiler I8, and an image-reproducingdevice l1.

For developing saw-tooth waves for the scanning elements included incathode-ray signal-reprosubject to oneor more oi plates 22 of ducingdevice i1, there are provided a line-frequency generator I9 and aheld-frequency generator- 2li. The output circuit of detector l5 iscoupled to a television scanning system for defiiecting a cathode-raybeam and including generators i9 and 20 for maintaining them insynchronism with the scanning system at the transmitter in aconventional manner. The output circuits of line-frequency generator I8are connected to f the scanning elements including electromagnetic gscanning winding 2| and electrostatic scanning device i1. similarly,'the dutput circuits or neidthe cathode-ray signal-reproducing'frequency generator 20 are connected to ileldfrequency electromagneticscanning winding 23 and held-frequency electrostatic scanning plates 24.Line-frequency electromagnetic scanning winding 2| and line-frequencyelectrostatic scanning plates 22 are relatively positioned so that theyprovide a cumulative deflection of the cathode-ray beam in theline-frequency scanning direction.` Similarly, held-frequencyelectromagnetic scanning winding 23and eld-frequency electrostaticscanning plates 24 are positioned for a cumulative deiiection of thecathode-ray beam in the held-frequency scanning direction.

Line-frequency scanning generator I9 comprises an oscillation generatorincluding a lowimpedance triode vacuum tube'25 and a. source ofunidirectional operating potential +B therefor, to which the anode oftube 25 is connected through a self-saturating reactor 26 in Vserieswith the anode winding of a feed-back coupling transformer 21. The gridwinding of feed-back coupling transformer 21 is coupled to the grid ofvacuum tube 25 and there is provided an additional winding on thetransformer 21 through which synchronizing impulses are applied tovacuum tube 25 from theoutput circuit of detector I5. The line-frequencyelectromagnetic scanning winding 2| are included in the anode circuitoi' vacuum tube 25 by way of saturating reactor 2l and blockingcondenser 3l. A suitable cathode-biasing-resistor 28, bypassed bycondenser 29, is provided for vacuum tube 25. There is also included inline-frequency scanning generator I9 a pentode vacuum tube 30 havinginput electrodes connected by way of a cathode-biasing resistor 3|,shunted by by-pass condenser 32, and blocking condenser 33 to the outputelectrodes of triode 25 through a wave form changing means comprising aseries-connected resistor 35 and condenser 31. The anode of pentode 36is connected by" way oi.' a load resistor 35 to the source ofunidirectional operating potential +B and is also connected by way oi' ablocking condenser 38 to one of the pair of line-frequency electrostaticscanning plates 22, the other of the scanning plates 22 being ygrounded.

The details oi.' the held-frequency scanning generator 20 have not beenshown and it will be understood that this generator may be constructedin a manner similar to that described for line-frequency generator I3.l

Coming now toan explanation of the operation of the system of Fig. i, itwill be understood `that the elements I-I5, inclusive, `may all be ofconventional well-known construction so that detailed illustrations anddescription thereof are deemed unnecessary herein. Briey described,however, signals intercepted by the antenna circuit iD, il are selectedand amplied in radiofrequency amplifier I2. and supplied to theoscillator-modulator I3 wherein they are converted tointermediate-frequency signals which are, in turn, selectively ampliiledin the intermediatefrequency amplifier I l and delivered to the dev, Themodulation components of the tector I5. signal are derived by detector Iand the videofrequency components are supplied to the videotrequencyamplier I6 wherein they are ampliiled and from which they are suppliedto the brilliancy-control element of the signal-reproducing device I1.'I'he intensity of the scanning beam of the image-reproducing device I1is with the video-frequency voltages impressed on its input circuit.

The saw-tooth scanning waves developed by the line-frequency generatori9 and held-frequency generator 20 and applied to the scanning elementsof cathode-ray reproducing device l1 cause the beam to be deflected soas to trace a rectilinear scanning pattern on the target ofthereproducing device I1 .and thereby reconstruct the transmitted image.The generators I9 and 20 are synchronized with the correspondingscanning apparatus at the transmitter by synchronizing pulses appearingin output circuits of detector I5, it being understood that suitablesynchronizing-signal separatingY circuits of a conventional form areincluded in the circuit of detector l5.

Referring now more particularly to the part of the system involving thepresent invention, the triode 25 generates oscillations at thelinescanning frequency of the system due to the feed-back couplingexisting between its grid and anode circuits through transformer 21, thefrequency of these oscillations being maintained constant by thesynchronizing pulses introduced into the input circuit of tube 25 fromdetector l5. The circuit constants of the relaxation osv cillatorincluding tube 25 are so related that thereby modulated or controlled inaccordance a voltage of rectangular wave form is produced at the anodeof tube 25 which is effective to develop current of substantiallysaw-tooth wave form in the line-frequency electromagnetic scanningwinding 2l,- the degree of linearity of this current during the traceinterval oi' the system being increased by saturating reactor 26 in amanner fully described in applicant/s British Patent No. 493,142,accepted October 5, 1938. By suitably proportioning the circuitconstants of the elementsassociated with tube 25, the current ofsaw-tooth wave form thro'igh the scanning winding 2l may readily be madeto provide about half the required deilection of the cathoderay beam ofimage-reproducing device I1 in the line-frequency scanning direction.

Vacuum-'tube 30 is provided in order to supply to line-frequencyelectrostatic scanning plates 22 a scanning voltage of substantiallysaw-tooth Wave form simultaneously with the application of the currentof saw-tooth wave form to scanping winding 2 l. Coupling network 36, 31serves to derive from the voltage of rectangular wave form` at the anodeof tube 25 a voltage of sawtooth wave form and of periodicity the sameas the saw-tooth current supplied to windirgs 2| which voltage appearsacross condenser 31 and is applied to the input circuit of vacuum tube,3o and which, after amplification thereby, is

Vapplied to the de ecting plates 22 of the cathoderay image-reproducingdevice I1. The windings 2| and the plates 22 are relatively positionedand energized to provide a cumulative deflection of the cathode-ray beamof reproducing device I1.

Since each of the electromagnetic and electrostatic scanning fieldscontributedl by generator I9 is of a magnitude usually provided inconnection with conventional relatively long cathode-ray tubes,suiiicient deflection of the scanning beam of a relatively shortcathode-ray tube can be obtained without resorting to high currentvalues in the scanning winding or to high potentials on the scanningplates with the attendant higher power requirements.

Fig. 2, in which circuit elements similar to those of Fig. 1, haveidentical reference numerals, is a circuit diagram of a modiedembodiment f of the invention wherein' two vpentode vacuum .nection 40to potential divider 4l, 42 across the output terminals of pentode 30.

A further embodiment of the modification shown in Fig. 2 is illustratedin Fig. 3, in which 'similar circuit elements have identical referencenumerals. The circuit of Fig. 3 differs from that of Fig. 2 only in thatthe input voltage for pentode 30' is derived by means of conductor Ildirectly from the input circuit of vacuum tube rather than from theoutput circuit of vacuum tube as inFig. 2.

In the above examples, it has been assumed that a substantially linearsaw-tooth current lis applied to scanning winding 2l and that asubstantially linear saw-tooth voltage is applied to electrostaticscanning plates 22. Due to the resistance ofthe scanning winding 2i andto the resistances of the coupling circuit between tubes 25 and 30,these ideal conditions will not actually obtain and there willresultsome slight nonlinearity during the trace interval in each of thesaw-tooth scanning wave forms these nonlinearities being oi' oppositesense. By properly proportioning the resistance ofthe scanning winding2l and the resistance and capacitance of the coupling elements betweentubes 25 and 30, the eiTect of these deviations from linearity duringthetrace interval can be made substantially to compensate one another.In other words, an effective resultant scanning ileld which is linearduring the trace interval is provided, even though neither the magneticcomponent nor the electrostatic component is linear during the traceinterval.

In Fig. 4 there is shown a modification of the invention in which only asingle triode vacuum tube is employed in the oscillator. Circuit elemntswhich are similar to those of corresponding elements of the precedingilgures have identical reference numerals; The saw-tooth An inputvoltage of opposite phase' current for electromagnetic scanning winding2l is derived from the output of vacuum tube 25 in the manner describedin detail above. However, in the modification of Fig. 4 the pentodeamplifier i`s omitted and a voltage of saw-tooth wave form forelectrostatic scanning plates 22 is derived directly from the outputcircuit of vacuum tube 25 by means of an integrating resistor-.condensercombination including a resistor 44 and a condenser 45, series-connectedacross the output circuit of vacuum tube 25. The embodiment of Fig. 4requires a higher value of current in the scanning winding 2| than dothe other embodiments described, but the saving of an amplifier stageeffects a saving in manufacturing cost.

While there have been described what are at 'suchI changes 'andmodiilcations as fall within the true spirit and scope of the invention.

What is claimed is: 1. A television scanning system for defiecting acathode-ray beam' comprising, an oscillation generator, electromagneticscanning windings,

means including said generator for producing a current of substantiallysaw-tooth wave form in said windings, electrostatic scanning plates,

and means including said generator for supplying to said platessimultaneously with said sawtooth current, a scanning voltage ofsubstantially saw-tooth wave frm and of periodicity the same n as saidsaw-tooth current, said windings and said plates being relativelypositioned to provide a cumulative deflection of the cathode-raybeam.

2. A'television scanning system for deecting a cathode-ray beamcomprising, an oscillation generator including a synchronizing 4circuitadapted to be excited by input synchronizing pulses, electromagneticscanning windings, means including said generator for producing acurrent oi' substantially saw-tooth wave form in said windings,electrostatic scanning plates, and means including said generator forsupplying to said plates simultaneously with said 'saw-toothv current, ascanning voltage of substantially saw'- tooth wave form and oiperiodicity the same as said saw-tooth current, said windings and saidplates being relatively positioned to provide a cumulative deection ofthe scanned cathoderay beam. y

3. A television scanning system for deilecting a cathode-ray beamcomprising. an oscillation generator including a low-impedance triodehaving inductively coupled input and output circuits, electromagneticscanning windings, means including said generator for producing acurrent of substantially saw-tooth wave form in said windings,electrostatic scanning plates, and means including said generator forsupplying to said plates simultaneously with said saw-tooth current, ascanning voltage of substantially s awtooth wave form and of periodicitythe same as said saw-tooth current, said coils and said plates beingrelatively positioned to provide a cumulative deilection of the -scannedcathode-ray beam.

v 4. A television scanning system for deflecting a cathode-ray beamcomprising, an oscillation generator for providing an output current ofsaw-tooth wave form and an output voltage of with the application ofsaid current of sawtooth wave form to said scanning windings, saidwindings and said plates being relatively positioned to provide acumulative deflection4 of the scanned cathode-ray beam. n

5. A television scanning systemA for deflecting a cathode-ray beamcomprising, an oscillation generator, electromagnetic scanning windings,means including said generator for producing a current of substantiallysaw-tooth Wave form in said windings, electrostatic scanning plates, avacuum-tube amplier, andl means including said generator and saidvacuum-tube amplifier for supplying to said plates, simultaneously withsaid saw-tooth current, a scanning voltage of substantially saw-toothwave form and .of pe'- riodicity the came as said saw-tooth current,said windings and said plates being relatively positioned 'to provide acumulative deflection of the scanned cathode-ray beam. y

6. A television scanning system for deecting a cathode-ray beamcomprising, an loscillation generator, electromagnetic scanningwindings, means including said generator for producinga current ofsubstantially saw-tooth wave form in said windings, electrostaticscanning plates, and means including said generator and two vacuum tubeshaving a balanced output circuit connection forsupplying to said plates,simultaneously with said saw-tooth current, a balanced scanning voltageof substantially sawtooth wave form and of periodicity the same as saidsaw-tooth current, said windings and said plates being relativelypositioned to provide a cumulative deilection of the scanned cathode-raybeam.

7. A television scanning system for deflecting a cathode-ray beamcomprising, an oscillation generator, electromagnetic scanning windings,means including said generator for producing a current in said windingsof substantially sawtooth wave form, having relatively long traceintervals, and being subject to slight deviations from linearity duringsaid trace intervals, electrostatic scanning plates, and means includingsaid generator for supplying to said plates, simultaneously with saidsaw-tooth current, a voltage of substantially saw-tooth wave form and fperiodicity the same as said saw-tooth current,

said voltage having relatively llong trace intervals and being subjectto slight deviations from linearity during said trace intervals of-opposite sense to that of said saw-tooth current. said windings andsaid plates being relatively positioned to provide a cumulativedeflection of the scanned cathode-ray beam, and the circuit constantsoi' said generator being so proportioned that the eiect of saiddeviations from linearity during said trace intervals substantiallycompensates one another.

8. A television scanning system for deecting a cathode-ray beamcomprising, an oscillation generator including a single vacuum tube,electromagnetic scanning windings, means including' said generator' forproducing a current oi' substantially saw-tooth wave form in saidwindings, eelctrostatic scanning plates, and wave form changing meanscoupled to said generator for supplying to said plates, simultaneouslywith said saw-tooth current, a scanning voltage of substantiallysaw-tooth form and of periodicity the same as said saw-tooth current,said windings and said plates being relatively positioned to provide acumulative deilection of the scanned cathode-ray beam.v

MAURICE K. TAYLOR.

